Process for dehydrogenating hydrocarbons



Sept 11, 1945. wfAfscHULzE PROCESS FOR DEHYDROGENATING HYDRCARBONS Filed Aug. 24,v 1940 lull INVENTOR W. A. SCHULZE ATTORN HOLVNOI .LDVtL-l Patented Sept. 11, 1945 rnocnss Fonpgmnoennn'rmc muecannous Delaware l"'iomai..incarner u annotation ofy Application August 24, 1944i,4 serial Nu. 354,085 vc claims. (ci. ceo-ssn) This invention relates to the dehydrogenation of hydrocarbons'and particularly to improved catalytic methods of dehydrogenating olenic hydrocarbons to -produce the corresponding diolens.

In a more specic sense the invention is concernedwith a new and improved process for controllably increasing the degree of unsaturation in `hydrocarbons of the character ,mentioned while reducing greatly the loss of valuable raw materials and products due to polymerization and decomposition reactions which normally occur at a rapid rate in the eiliuents from the catalytic treatment.

In the production of butadiene, for example, by the catalytic dehydrogenation of butenes, serious losses may occur because of decomposition reactions. When this treatment is carried out at atmospheric pressures, large quantities of light gases are produced, coke is deposited on the catalyst in quantities suicient to plug the catalyst tubes, and considerable liquid polymer is formed.

The recovery of diolefin under these conditions is very small, and operating diiiiculties often result in exceedingly brief operating periods.

It is possible to suppress these undesirable side reactions to a large extent by operating the dehydrogenation with partial pressures of butenes in the range of 0.1 to 0.5 atmospheres through the use of inert diluents. Under these conditions,

polymerization and cracking of 'both oleiins and dioleilns within the catalyst space is reduced sul-' ci :tly so that in many cases the process may be operable.

It is also Ypossible to suppress decomposition l and polymerization reactions by special treatment of the catalyst toreduce the promotion of side reactions. By this/means the dehydrogenation of butenes may be carried out with a. minimum ci cracking and polymer formation within the catalyst space.

However, even in these above-described improved processes wherein side reactions are minimized during the period of actual contact oi hydrocarbons with the catalyst, considerable loss of oleiins and dioleiins occurs due to the formation of liquid polymer after the eiiluents emerge from the catalyst bed. The vapors leaving the catalyst at' temperatures of 1100 to 1300 F. may contain only traces of polymer, but rather high percentages ofliigli-boiling polymers are found in the dehydrogenated vapors after cooling to temperatures in the range of 15G-300 F. 'I'he polymerization reactions involved may be illustrated,

using general formuladas follows:

Monomerzrldimerz-Zhigher polymers At high temperatures of the order of 1000 F'.

.equilibrium is established in extremely short tlmes, .but the concentrationsof dimer and higher longperiods of time.

polymer at equilibrium are very small. At low temperatures of the order of 200-300 F., the equilibrium is established so slowly that little dimer is normally formed even though equilibrium concentrations allow the formation of high percentages. At intermediate temperatures, however, both the time required to establish equilibrium and the equilibrium concentrations are favorable to dimer and higher polymer formation.

For example, at temperatures around 1200 F.

the quantity of dimer formed at equilibrium from butenes is less than one per cent, but this quantity increases to about 5 per cent at temperatures near 700 F. Butadiene is even more readily polymerized, and at temperatures of 700-1000" F. a very considerable quantity of the diqlen may exist in the dimeric form at equilibrium. Copolymers formed between butenes. and butadiene are also more readily formed than .butene polymers,

and may account for a further amount of polymer formation. I'hus I have found that serious losses of butadiene may occur subsequent to the catalytic dehydrogenation step while the effluent vapors are being cooled if suiiicientzftime elapses for equilibrium concentrations of polymers to be attained in the temperature range of rapid polymei-ization.

The polymerization reaction velocity is enormously greater at temperatures Just below the dehydrogenation range than it is at low temperatures such as those finally attained by the cooling system. Consequently, the formation of large amounts of polymer in the cold eilluents does not occur in the absence of catalyst, even over very On the other hand, in the range from dehydrogenation temperatures down to about 600-800 F. polymerization reaction rates are still extremely high so that equilibrium concentrations are approached in a few seconds or wless. The large quantities of polymer formed 4- 700 F.` the reaction velocity of polymerization becomes too small to cause measurable losses,

even when the cooling period is prolonged.

I have noted that when carrying out the dehy- .drogenation of butenes quantities of polymer varying from about two to about ten -per cent of the butene charge are often formed while conversion to butadiene is of the order of about fourteen to twenty four'per cent. Thus, the loss of diolein due to polymerization which may largely occur after the eilluent vapors leave the catalyst may be seen tube very serious;

I have now foundthat the quantity of butadiene converted to liquid polymers and tar may be very greatly reduced andthe yield oi' butadiene markedly increased if the. hot effluent vapors *bey cooled immediately on their emergence from the catalyst by injection of considerable proportions of cold liquid hydrocarbons so that the temperature of the stream is almost instantly reduced to such a temperature that the rate of polymerization is low. I haveiound that it is possible by this procedure to pass through that temperature range where the rate of polymerization is high and the quantity of polymer at equilibrium is appreciable in such a short time that essentially no further polymerization takes place after'theI efiiuent vapors leave the catalyst. Thus I am able to freezel the vapor composition at the 4, compressor l and condenser l into accumulator 1. Sunicient cooling and/or refrigeration is applied in I to make possible a satisfactory separation of C: hydrocarbons and lighter material as gases from the Ca, and C4 hydrocarbon liquid in 1, with only small losses to C: hydrocarbons.A The cooledf liquid then passes direct to butadiene separator 9 wherein the butadiene is" extracted and the remaining C: and C4 material is returned, partly to the fresh feed line as recycle and partly to the quench injection lines. Sufficientv fresh butene charge is added to the recycle material to maintain the desired partial pressure in the charge to the catalyst, and sumcient propane diluent isadded to compensate for any propane converted or'lost in the process.

limits the choice as well asrdo the factors of heat stability and of thermal properties.

'I'he process according to the invention may be more readily understood with reference to the accompanying drawing, which represents schematically one form of apparatus in which it may be carried out. In the gure, I is a heater into which thebutenes diluteiiwith propane are rst led and vaporized. Leaving the heater, the heated vapor enters catalyst chamber 2, where it con- Y tacts a suitable dehydrogenation catalyst. 'Ihe temperature of thebottom section oi the catalyst bed is maintained near that of the top section. Immediately below the catalyst cases or below the catalyst sections in the cases. liquid propanev is injected into the stream. This. combined partially cooled vapor stream then passes to coolin! system 3, composed of suitable combinations of condensers, heat, exchangers and the like where cooling is complete, and any liquid polymer is separated in polymer separator 4. The vapors then enter compression unit i, and after compression pass to coolers i and accumulator 1. Light gases` are removed from the accumulator 1 while the liquid hydrocarbons pass to iractionating column 8. Propane is removed overhead through condenser I0 and accumulator Il, from which part of the condensate is returned as reflux to the column. The excess condensate passes to propane-storage i2. Part oi' the propane from i2 is recycled as' a. diluent gas in thedehydrogenation step, and part is available for-'further use as acooling agent. The C4 hydrocarbons from the fractionator kettle pass tobutadiene separator 9-inwhich butadiene is separated i'rom the mixed butenes and sent to storage. V'The butenes are recycled for further treatment.

An optional method of operation according to' the figure eliminates the separation of Ca and C4 hydrocarbons in fractionating column l. The

butene, charge 'diluted with propane vpasses through heater land catalyst chamber 1 as in the previously described operation 'I'he direct -In operating my process for the production of butadiene, either of the normal butenes or any convenient or available mixture of them may be used as charge stock with satisfactory results. In many cases dehydrogenation of the olei'in will iollow as the second stage to a similar dehydrogenatlon step applied to butane.' The mixedbutenes derived from cracking still gases or other sources are also satisfactory charges if substantially free of heavy material.

The temperature of the catalytic treatment will depend somewhat upon the catalyst selected, but temperatures within the range o f 1100 to 1400 F. are usually necessary to achieve satisfactory conversions to diolenns. With active catalysts iiow rates of 1 to 10 liquid volumes of charge per hour per volume of catalyst are ordinarily satisfactory, although higher rates may be used.

`It is necessary to maintain the partial pressure of butene below atmospheric, ordinarily in the range of 0.1 to 0.50 atmosphere. This may be accomplished by vacuum operation, if desired, but is most readily accomplished by dilution with an linert gas. In this way atmospheric or slightly higher pressure may be maintained through the treating? system. In some cases the use'of pressures considerably above atmospheric, up to two or threehundred pounds gage, may be advan-` tageous in processing, the emuent vapors.

Diluent gases which may ordinarily A be employed for the dehydrogenation step comprise the hydrocarbons more refractory than butenes. par- `ticularly propane and other in t gases. espe- 'ticularly suitable is a specially 'treatedv bauxite quenching is accomplished by iniection of reof the recycle liquid from buta- 9 comprising propane. propyleiii quired amounts diene extractor and butenes. .The eilluents are further cooled exchanger 3 and pass through polymer separator 754 equilibrium value may cially carbon dioxide and nitro n.v `The choice of. diluent is considerably affected in my new process by the injection oi a hydrocarbon gas for rapid cooling of the emuents subsequent to treatment. Preferably the same gas is used for both purposes thereby greatly simplifying the subsequent` separation steps and recycling arrangements. I prefer to use propane, or more generally,at least a fairly close cut Ca fraction comprising propane.and/or propylene for this purpose.. The propaneand/or propylene may be ob-n tained from any desired source. y

The catalyst employed may be selected `from those of suitable dehydrogenating activity. Parcatalyst in which deactivation toward polymerization and cracking reactions has beeneilected by chemical treatment. I find that any polymer formed within 'the catalyst 'space may be4 readily cracked to give a carbon deposit andlarge volumes`of hydrogen and light gases at the high temperature of operation, Although the quan- `tity of lpolymer which can be present is fixed at a small'va'iue by equilibrium conditions at dehydrogenatingtemperatures Imaintenance of this ieaaltosseripusiou u the temperature from 700 F. to 100 F. About 0.4 to 0.5 per cent polymer was separated in the polymer separator during the nal cooling. After fractionation and separation of butadiene, 21% of the volume of butene charged was obtained as butadiene, and sixty per cent of butenes was recovered unchanged. and recycled.

A test conducted under identical conditions but without injection of liquid propane for cooling yielded only 17 per cent of the butene as butadiene, while liquid .polymer separated reached 4 per cent.

l While my process has been described specifically in connection `with the production of butadiene from butenes, I have found that it is of generally wide scope and satisfactory application to the dehydrogenation of other hydrocarbons of the character mentioned to controllably increase the unsaturation without altering the carbon atom structure of the hydrocarbon molecules.

E claim:

l. A process for the production ,of butadiene which comprises catalytically dehydrogenating butenes admixed with C: hydrocarbons to produce a partial pressure of butenes below 0.5 atmosphere at temperatures between 1000 and 1300 F. so that a considerable proportion of the butenes is converted to butadiene, injecting into the efiiuentl vapors adjacent the point of exit from the catalyst space sumcient recycle liquid comprising Ca' and C4 hydrocarbons to redu :e the tempera:-

ture thereof below the range of rapid diolefin,

,to the catalyst.

K :,'38-l=,45 r

" suiilcient liquid propane to reducel the. vapor stream temperature below about 750 F., compressing and condensing the eflluents with separation of light gases, fractionating the condensate to produce. a C3 hydrocarbon overhead fraction which is returned for use as diluent and coolant and a C4 hydrocarbon bottoms fraction, processing Ithe said C4 hydrocarbon fraction to extract butadiene therefrom, and finally recycling the unconverted butenes along with fresh butene feed 4. A process for the production of butadiene which comprises catalytically dehydrogenating butenes diluted with @s hydrocarbons to produce a partial pressure of butenes in the range of 0.1 to 0.5 atmosphere at temperatures between 1000 and 1300 F'. and pressures of zero to 50 pounds gage, injecting into the hot eiiuent vapors adjacent the point of exit from the catalystspace sumcient recycle liquid comprising Cs and C4 hydrocarbons to reducethe vapor stream` temy perature below albout 750 F., compressing and condensing the. eiiluentswith separation of material lower-boiling than Ca hydrocarbons therefrom, processing the condensate to extract/butadiene and finally recycling the substantially diliquid propane to reduce the temperature below the range of rapid diolefin polymerization, compressing and condensing the eluents with separation of light gases, fractionating the condensate to remove C: hydrocarbons overhead and a 45 C4 hydrocarbon bottom fraction, recycling prodiluent in contact with a dehydrogenating catl alyst at temperatures between 1000 and 1300 F. so that a considerable proportion of the butenes is converted to butadiene, cooling and condensing the effluents to separate' light gases from the C3-C4 condensate, processing said condensate to extract butadiene therefrom and recycling the substantially butadiene-free liquid to the catalytic treatment, the step of injecting into 'the hot effluents from the catalyst space sumcient of the recycle Ca--C4 liquid to reduce the vapor temperature below the range of rapid diolefin polymerization, thereby suppressing polymerization of the unsaturated components of the emuent vapor during the cooling period and increasing theprocess yields of butadiene.

a partial pressure ofbutenes in the range of 0.1

to 0.5 atmosphereat temperaturesbetween 1000"' and 1300 F., injecting into the hot eilluent vapors adjacent the point of exit from the catalyst space pane from the C: overhead fraction to the dehydrogenation for admixture with the butene as diluent and for injection into the eiiluent as coolant, separating butadiene from the C4 hydrocarbon bottoms fraction, and finally recycling the unconverted butenes to the catalytic treatment.`

6.. A process for the production of a straight chain diolefin by dehydrogenation of the corre- 4subjecting the mixture to conditions of 'dehydrogenation under which at least a portion of the.

olefin is converted into the corresponding diolen, injecting into the eiiiuent of the dehydrogenation immediately following dehydrogenation an additional quantity of saidhydrocarbon diluent in liquid phase suiiicient to reduce the temperature of the eluents Ibelow thev range of rapid dioleiin polymerization, recovering the diolefns from the cooled eilluent, and recycling diolen-free eiliuent containing the hydrocarbon diluent to the dehydrogenation for admixture with the oleiins and for cooling of the eiiiuent of the dehydrogenation.

WALTER. A. scHULzE.

.pressed by the retained propylene.

a catalyst with active cracking properties' is employed and the advantage of the subsequent direct quenching may thus be partially nulliiied.

The catalyst chambers 'may be of various sizes and designs, as will be evident to those skilled in the art, but' should be'so constructed and operated that no portion of catalyst is in a zone in which the temperature is below the range used for conversion. 1f the temperature of the vapors is allowed to drop substantially while in contact with catalyst, polymerization may take placeat an extremely rapid rate before my quenching step can be applied. It will be noted that all the tions under which the dehydrogenation process are preferably operated are so selected as to minimize the formation and subsequent decomposition of polymer in the catalyst space and to give a foregoing condimaximum yield of butadiene and recovery of unconverted butenes at the point of emergence from the catalyst space.

` For carrying out the very rapid quenching step I prefer to employ liquidpropane ior propylene or mixtures thereof, or the Ca-C4 material remaining after the extraction of butadienewhen only ethane and lighter material isremoved from the` eflluents from the catalyst.- Propane is extremely satisfactory since a column for deproiluent vapors undergoing cooling. However, va-

por lines oi.' sumcient size to avoid increase in pressure must be provided at' this point.

The quantityof coolant injected will depend -500 to 900 F. but I find that a temperature near 700 F. is ordinarily suiiicient and not too dimcult to attain. Thus, a drop of about 400 to 500 E. is brought about when dehydrgenating near 1200 F., reducing the velocity of polymerization enormously. 'This amount of cooling may be ordinarily achieved by injection of coolant in quantities equivalent to and often much less than panizing the eiiluent stream is Aordinarily provided to separate the propane diluent. Thus, the sep' aration of additional propane presents no further problems. Propane may readily be liquefied and pumped, and expands to a gas with absorption ofconsiderable quantities of heat. `Ethane is muchkmore troublesome to compress andhandle" and is thereforenot convenient for use except in limited instances. Butane on'the other hand, while readily compressed and handled, is not `readily separated from the mixed predominately unsaturated C4 hydrocarbons resulting from the' dehydrogenation process; Onlyvery small concentrations of butane can be tolerated in the recycle butene stream, and segregation Aof butane from butenes would require an additional costly processing step. Higher hydrocarbons of five or more carbon atoms are not ordinarily applicable because of instability at high temperature.

When it is desired to process the total eiiluent stream to extract butadiene without separating the C: and C4 hydrocarbons, the recycle stream is entirely satisfactory for my quenching step. 'I'he propane, obviously, is suitable and the unsaturated C4 .hydrocarbons are not heated to a temperature high enoughl to initiate polymerization. The utilization of a secondary internal recycle is of particular benet in that less propane is required from an external supply, and that any propylene formed is largely retained within the system with consequent advantages to the dehydrogenation step. These last-named advantages are derived from the greater heat stability of propylene and the fact that lthe production'of small amounts of hydrogen from propane is sup/ 'I'he coolant is best injected into the eilluent 68 vapors as near as possible to the point of exit from the catalyst bed without cooling the vapors V still in contact with the catalyst. Valves must of course be so constructed as to prevent freezing.- In general. conductance of heat from the acted by the simultaneous contraction of the et- 76 that of the original eilluents'. The degree of conversion influences the quantity needed slightly, due to the increase in volume of gases accompanying increased conversion. The latent heat ofyaporization of the propane, and/or butenes as well as the generally greater temperature gradient through which it is heated compared with the coolingv vapors make the quantity of coolant required generally about one half to two thirds of the volume of the ellluent vapors.

The quenching is accomplished almost instantaneou'sly and there is no chance for polymerization to follow'the equilibrium curve as the temperature is lowered. Generally, equilibrium concentrations of `polymer at 1200 F., ordinarily much less than one per cent, are present in the eilluent vapors treated according to the present invention. The polymer concentration is thus fixed at this value during cooling to about 700 F.. At this temperature and below polymerization is very much slower. It is thus possible to pass the partially cooled vapors through further heat exchangers, condensers, polymer separators and other equipment of conventional cooling systems, without further appreciable polymer formation regardless of the time required.

The separation of light gases alone or of the light gases and the total quantity of Ca material from the eiliuents may be carried out on conventional lines, obvious t'o those skilled in the art. The C: hydrocarbon stream may be recycled as a diluent in proper volume, the emainder being separated and recycled as coo nt. `Any excess The following example will serve to more fully illustrate the results which may be obtained by my invention,'although said example is not to be construed as a limitation thereof.

Example Butene-l produced by the dehydrogenation or butane was diluted with 3` volumes ofa propane- Vpropylene fraction and processed in the equipment shown in the ligure. The catalyst was calcined 6-14 mesh bauxite treated with 5%' barium hydroxide. I'he gas was treated' at 11'15" F. and 5 pounds gage pressure. Conversion to butadiene was ner 20% and the polymer content ot the hot vapor stream leaving the catalyst was less than 0.5 liquid volume per cent;y Propane at F. equivalent in gaseous form to 2.75 .volumes of the 

